In recent years, new types of laser light sources using a photonic crystal have been developed. A photonic crystal consists of a dielectric body material in which an artificial periodic structure is created. Usually, the periodic structure is created by providing the body material with a periodic arrangement of areas whose refractive index differs from that of the body material (this area is hereinafter called the “modified refractive index area”). The periodic structure causes a Bragg diffraction within the crystal and creates an energy band gap for the energy of light. There are two types of photonic crystal laser light sources: one utilizes a band-gap effect to make a point-like defect function as a resonator, and the other utilizes a standing wave at a band edge where the group velocity of light becomes zero. Each of these devices causes a laser oscillation by amplifying light of a predetermined wavelength.
Patent Document 1 discloses a laser light source in which a two-dimensional photonic crystal is created in the vicinity of an active layer containing a luminescent material. The two-dimensional photonic crystal includes a plate-shaped semiconductor body in which cylindrical holes are periodically arranged (e.g. in a triangular, square or hexagonal lattice pattern) so as to provide the crystal with a two-dimensional, periodic distribution of refractive index. The cycle distance is adjusted so that it equals the wavelength of light to be generated within the active layer by an injection of carriers from an electrode. As a result, a two-dimensional standing wave is produced within the two-dimensional photonic crystal, whereby the light is strengthened to produce a laser oscillation.
When the two-dimensional standing wave is produced, the light within the two-dimensional photonic crystal (this light is hereinafter called the “internal resonance light”) partially leaks from the side portion of the two-dimensional photonic crystal. This leads to an energy loss and accordingly lowers the lasing efficiency. Furthermore, the leaked light is absorbed by the active layer and generates heat. These phenomena undesirably cause an increase in the minimum level of the current capable of producing the laser oscillation (“threshold gain”).
Patent Document 2 discloses a two-dimensional photonic crystal surface emitting laser light source in which a member for reflecting the internal resonance light is provided around the two-dimensional photonic crystal. The document claims that this structure prevents the internal resonance light from leaking from the side portion of the two-dimensional photonic crystal and thereby improves the light use efficiency.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-332351 (Paragraphs [0037] through [0056] and FIG. 1)
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2003-273456 (Paragraphs [0023] through [0026] and FIG. 1)